Hydrogen-containing electrically conductive inorganic compound

ABSTRACT

Disclosed is a 12CaO.7Al 2 O 3  compound, a 12SrO.7Al 2 O 3  compound, or a mixed crystal compound of 12CaO.7Al 2 O 3  and 12SrO.7Al 2 O 3 , which contains a negative hydrogen ion (H − , H 2− , H 2   −  at a concentration of 1×10 18  cm −3  or more. A negative hydrogen ion comprising a primary component of a hydride ion is incorporated into C12A7 (12CaO.7Al 2 O 3 ), so that a function of being converted from an insulative material to an electrically conductive material in a sustained manner by means of irradiation with light can be exhibited even in the normal atmosphere at a room temperature. The present invention also provides a solid electrolyte capable of conducting a negative hydrogen ion, and means for releasing a hydride ion from the inside of a solid into a gaseous phase using an electric field.

TECHNICAL FIELD

The present invention relates to a 12CaO.7Al₂O₃ compound (hereinafterreferred to as “C12A7”), a 12SrO.7Al₂O₃ compound (hereinafter referredto as “S12A7”), or a mixed crystal compound of 12CaO.7Al₂O₃ and12SrO.7Al₂O₃, which contains a negative hydrogen ion. The presentinvention also relates to a production method for these compounds, andthe uses of these compounds.

BACKGROUND ART

Heretofore, there has been known only a few solid inorganic materialscapable of being converted from their normal state or an insulativematerial to an electrically conductive material by means of irradiationwith light. Recently, as one of the few cases, it was reported thatyttrium hydride (YH_(x)) or lanthanum hydride (LaH_(x)) can be convertedfrom an insulative state to an electrically conductive material in asustained manner by means of irradiation with ultraviolet ray (A. F. Th.Hoekstra et al., Phys. Rev. Lett. 86[23], 5349, 2001).

In 1970, H. B. Bartl et al. found out that a C12A7 crystal has an uniquefeature in which among 66 oxygens residing in a unit cell including twomolecules, two oxygens are not included in a network but exist as “freeoxygens” in the inner space of cages residing in the crystal (H. B.Bartl and T. Scheller, Neues Jahrb. Mineral., Monatsh. 1970, 547). Untilnow, it has been verified that the free oxygens can be substituted withvarious types of negative ions.

Based on the measurement of electron spin resonance, Hosono who is oneof the inventors of the present invention, et al. found out that CaCO₃and Al₂O₃ or Al(OH)₃ can be used as a raw material and synthesizedthrough a solid-phase reaction at a temperature of 1200° C. in the airto obtain a C12A7 crystal clathrateing O₂ ⁻ at a concentration of about1×10¹⁹ cm⁻³. They proposed a model such that a part of free oxygensexists within crystal cages in the form of O₂ ⁻ (H. Hosono and Y. Abe,Inorg. Chem. 26[8], 1193, 1987, pp. 171-172, 1996, Materials ScienceSociety of Japan).

The inventors newly found out that a raw material prepared by mixingcalcium and aluminum at the atomic equivalence ratio of about 12:14 canbe subjected to a solid-phase reaction under a controlled temperatureand atmosphere to obtain a C12A7 compound incorporating active oxygenspecies at a high concentration of 10²⁰ cm⁻³ or more. The inventorsfiled a patent application for inventions concerning the compounditself, a production method therefor, means for extracting incorporatedions, a method for identifying the active oxygen ion radicals, and theuses of the compound [Japanese Patent Application No. 2001-049524(Patent Laid-Open Publication No. 2002-003218), PCT/JP01/03252(WO0179115-A1)].

Subsequently, the inventors found out a method of controlling theconcentration of an anion other than a negative oxygen ion, such as OH⁻ion in a C12A7, to incorporate or extract active oxygen species at about700° C., and filed a patent application for inventions related thereto[Japanese Patent Application No. 2001-226843 (Patent Laid-OpenPublication No. 2003-040697)]. The inventors also found out that aelectric field can be applied to a C12A7 compound containing an activeoxygen at a high concentration to extract a high-density O⁻ ion beam,and filed a patent application for inventions related thereto [JapanesePatent Application No. 2001-377293 (WO 03/050037A1)].

Furthermore, the inventors found out that a C12A7 compound powdersubjected to a hydration reaction in water, water-containing solvent orwater-vapor-containing gas can be burnt in an oxygen atmosphere tosynthesize a C12A7 compound containing an OH⁻ ion at a concentration of10²¹ cm⁻³ or more, and filed a patent application for inventionsconcerning the compound itself, a production method therefor, a methodfor identifying the OH⁻ ion, and the uses of the compound [JapanesePatent Application No. 2001-117546 (Patent Laid-Open Publication No.2002-316867)].

A 12SrO.7Al₂O₃ compound (S12A7) is known as a material having a crystalstructure similar to that of a C12A7 compound (O. Yamaguchi et al. J.Am. Ceram. Soc. 69.[2] C-36, 1968). As to a S12A7 compound, theinventors also filed a patent application for inventions concerning asynthetic method therefor, a method for incorporating an active oxygenion and the uses of the compound [Japanese Patent Application No.2002-045302 (Japanese Patent Publication No. 2003-0238149)].

DISCLOSURE OF INVENTION

The aforementioned yttrium hydride (YH_(x)) and lanthanum hydride(LaH_(x)) have difficulties in practically utilizing their electricallyconductive properties, due to the need for maintaining them at a lowtemperature of 200 K or less to assure their electrically conductivestate in a sustained manner, and very poor stability causing rapiddecomposition in the normal atmosphere.

Through various researches on new possible negative ions to beintroduced in C12A7, the inventors found out that a C12A7 compound heldin a high-temperature hydrogen flow is stained green by irradiation withultraviolet ray, wherein in concurrence with the coloring, the12CaO.7Al₂O₃ compound, which is originally an insulative material, isconverted to an electrically conductive material in a sustained manner,and then the electrically conductive state can be re-converted to theoriginal insulative state by means of heating or irradiation with strongvisible light.

As the result of further studies, it was proved that this phenomenon isoriginated from a negative hydrogen ion introduced in the C12A7 crystal.It was also found that the negative hydrogen ion itself exhibits ahigh-speed ionic conductance, and the negative hydrogen ion can beextracted into a vacuum space by means of electric filed. In thisspecification, the generation of a current arising from transfer ormigration of electron or negative ion is defined as “electricconductance”, wherein if it is clear that either one of electron andnegative ion plays a major role in generating a current, it is referredto as “electronic conductance” and “ionic conductance”, respectively.

The present invention has been made based on the above knowledge. In thepresent invention, a negative hydrogen ion (H⁻, H²⁻, H₂ ⁻) comprising aprimary component of a hydride ion H⁻ is incorporated in C12A7 which isa stable solid material capable of incorporating various types ofnegative ions, to provide a material capable of exhibiting a function ofbeing converted from an insulative material to an electricallyconductive material in a sustained manner by means of irradiation withlight in the ultraviolet or X-ray region, even in the normal atmosphereat a room temperature.

Specifically, the present invention is as follows.

(1) A 12CaO.7Al₂O₃ compound, which contains a negative hydrogen ion (H⁻,H²⁻, H₂ ⁻) at a concentration of 1×10¹⁸ cm⁻³ or more.

(2) A 12SrO.7Al₂O₃ compound, which contains a negative hydrogen ion (H⁻,H²⁻, H₂ ⁻) at a concentration of 1×10¹⁸ cm⁻³ or more.

(3) A mixed crystal compound of 12CaO.7Al₂O₃ and 12SrO.7Al₂O₃, whichcontains a negative hydrogen ion (H⁻, H²⁻, H₂ ⁻) at a concentration of1×10¹⁸ cm⁻³ or more.

(4) The compound set forth in either one of (1) to (3), which has anelectronic conductance equivalent to an electric conductivity of 10⁻⁵Scm⁻¹ or more.

(5) The compound set forth in either one of (1) to (3), which exhibits asustained increase in electronic conductivity by means of irradiationwith ultraviolet ray or X-ray, and has an electric conductivity which isreversibly changed by means of irradiation with light.

(6) The compound set forth in either one of (1) to (3), which has anionic conductance.

(7) A method of producing the compound set forth in either one of (1) to(3), comprising subjecting either one selected from the group consistingof a 12CaO.7Al₂O₃ compound, a 12SrO.7Al₂O₃ compound, and a mixed crystalcompound of 12CaO.7Al₂O₃ and 12SrO.7Al₂O₃ to a heat treatment at atemperature of 800° C. or more in an atmosphere containing 1000 ppm ormore of hydrogen, to thereby incorporate a negative hydrogen ion (H⁻,H²⁻, H₂ ⁻) into the selected compound at a concentration of 1×10¹⁸ cm⁻³or more.

(8) A transparent electrode or wiring, which is formed using thecompound set forth in (4) or (5).

(9) An optically writable and erasable 3-dimensional electronic circuitand 3-dimensional storage element, which is formed using the compoundset forth in (5).

(10) A negative hydrogen ion (H⁻, H²⁻, H₂ ⁻)-conductingsolid-electrolyte, which is formed using the compound set forth in (6).

(11) A method of generating a negative hydrogen ion or hydrogen gas,comprising applying a given voltage to the compound set forth in eitherone of (1) to (3), to thereby extract a negative hydrogen ion from thecompound.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a light absorption spectrum and the wavelengthdependence of light sensitivity in a single crystal obtained in Example1.

FIG. 2 is a graph showing the respective temperature dependences ofelectronic conductance and ionic conductance in a single crystalobtained in Example 2 (wherein the vertical axis represents thelogarithm of conductivity, and the horizontal axis represents the −¼power of absolute temperature).

FIG. 3 is a graph showing the respective changes of absorbance andelectric conductivity relative to temperature in a single crystalobtained in Example 3 (each value is normalized by a value at 25° C.).

FIG. 4 is a graph showing the measurement result of hydrogen molecule ina polycrystal sample obtained in Example 4, which is detected by athermogravimetric and mass spectrographic analysis.

FIG. 5 is a graph showing a method of quantitatively determining anegative hydrogen ion concentration shown in Example 5.

FIG. 6 is a graph showing an electron spin resonance spectrum of apolycrystal obtained in Example 6.

FIG. 7 is a graph showing a mass spectrum indicative of a hydride ionreleased from a polycrystal sample according to an electric fieldapplied thereto.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a starting material may be a pure C12A7compound, or may be a mixed crystal or solid solution having a crystalstructure equivalent to that of a C12A7 compound in which a part or allof calcium and aluminum are substituted with a different element(hereinafter referred to as “equivalent material” for brevity), unlessthe substitution causes destruction of the specific crystal structure ofC12A7.

A currently known material having a crystal structure equivalent to thatof a C12A7 compound includes 12SrO.7Al₂O₃, and the mixing ratio betweenCa and Sr can be freely changed. That is, the starting material may be amixed crystal compound of 12CaO.7Al₂O₃ and 12SrO.7Al₂O₃. The type andamount of a negative ion initially incorporated in the compound havelittle influence on the effect of introducing a negative hydrogen ion.The starting material may be prepared in any form, such as powder, film,polycrystal or single crystal.

C12A7 as a starting material is synthesized by preparing a raw materialcontaining calcium (Ca) and aluminum (Al) at the atomic equivalenceratio of 12:14, and subjecting the raw material to a solid-phasereaction at a burning temperature ranging from 1200° C. to less than1415° C. Typically, the raw material is a mixture of calcium carbonateand aluminum oxide.

A C12A7 single crystal can be obtained through a floating zone (FZ)process using a C12A7 sintered body obtained through a solid-phasereaction, as a precursor. Specifically, the rod-shaped ceramic precursoris pulled upward while focusing infrared light on the precursor to shifta molten zone so as to continuously grow the single crystal along theinterface between the molten zone and a solidified portion. Theinventors filed a patent application for inventions concerning a C12A7compound single crystal containing active oxygen species at a highconcentration and a method of producing a C12A7 single crystal free ofair hole [the aforementioned Patent Application No. 2001-226843 (PatentLaid-Open Publication No. 2003-040697)].

The prepared C12A7 or equivalent material as a starting material is heldin an atmosphere containing 1000 ppm or more of hydrogen, preferably theflow of an atmosphere containing 20 volume % of hydrogen without oxygenand water, at a temperature of 800° C. or more, preferably 1000° C. toless than 1350° C., more preferably about 1300° C., for several minutesto several hours depending on the form of the starting material, andthen cooled. The atmosphere containing hydrogen may be obtained byfilling hydrogen in a vessel made of a material, such as silica glass ortantalum, capable of withstanding a high-temperature heat treatment, andthe starting material may be hermetically contained in the vessel. Inthis case, instead of filling hydrogen gas, a material capable ofgenerating hydrogen through a chemical reaction may be encapsulatedtogether with the starting material. It is to be noted that if astarting material made of pure C12A7 is heated at 1350° C. or more, itwill be molten to cause destruction of its original crystal structure.

If the hydrogen in the atmosphere for the heat treatment is set at aconcentration of less than 1000 ppm, the concentration of a negativehydrogen ion introduced in the C12A7 or equivalent material will bereduced to less than 1×10¹⁸ cm⁻³, and therefore intended characteristicsof exhibiting an electronic conductance by means of irradiation withultraviolet ray or X-ray and having an ionic conductance derived fromthe negative hydrogen ion cannot be adequately obtained. Further, as thetemperature for the heat treatment is set at a lower temperature, thehydrogen ion to be introduced in the C12A7 or equivalent material isliable to be alternated with a hydroxyl ion (OH⁻). If the heat-treatmenttemperature is set at less than 800° C., the concentration of theintroduced negative hydrogen will be reduced to less than 1×10¹⁸ cm⁻³,and therefore the intended characteristics cannot be adequatelyobtained.

While the cooling process may be a usual self-cooling in an electricfurnace, it is preferable to quench or rapidly cool the heat-treatedmaterial. In particular, when the heat treatment is performed at arelatively low temperature, the heat-treated material is rapidly cooledto allow the concentration of the negative hydrogen ion to be 1×10¹⁸cm⁻³ or more.

The material after completion of the above high-temperature treatment isin an insulative material having an electric conductivity of 10⁻¹⁰ Scm⁻¹or less. When the starting material of the treated material is made ofpure C12A7, the treated material is transparent and colorless. Then, inresponse to irradiating the treated material with ultraviolet lighthaving a wavelength of about 300 nm, the conductivity starts increasing,and the irradiated material will exhibit an electronic conductance ofabout 1 Scm⁻¹ at the time the increase is saturated. When the startingmaterial of the irradiated material is made of pure C12A7, theirradiated material will concurrently have a color ranging fromyellowish green to dark green. FIG. 1 shows the change in opticalabsorption spectrum and the sensitivity to the wavelength of theradiated ultraviolet light in this irradiation process. FIG. 2 showsdata about electronic conductivity.

If the radiated light has a photon energy of less than 2 eV, it cannotact on the negative hydrogen ion, or cannot increase the electronicconductance. Further, if the radiated light has a photon energy of 5 eVor more, it cannot efficiently act on the negative hydrogen ion due tolight absorption of the C12A7 crystal itself. The heat-treated materialmay also be irradiated with X-ray having far higher photon energy. Inthis case, the C12A7 crystal itself does not absorb the light. Thus, theX-ray can act on the negative hydrogen ion to increase the electronicconductance and develop a color of dark green.

In response to the ultraviolet acting on the negative hydrogen ion, anelectron is released. The released electron is mildly confined within acage in the crystal in an F⁺ center-like state. The electron (conductioncarrier) of F⁺ center migrates within the crystal while hopping acrosscages to thereby generate an electron conductance. Such electronicallyconductive state is maintained in a sustained manner at a roomtemperature, and any significant change will not be observed even afterleft at the room temperature for one month. That is, a sustainedelectronic conductance can be obtained. A sufficient electronicconductance equivalent to an electronic conductivity of 10⁻⁵ Scm⁻¹ ormore can be generated only if the negative hydrogen ion serving as asource of the conduction carrier is contained in the treated material ata concentration of 1×10¹⁸ cm⁻³ or more, preferably 1×10¹⁹ cm⁻³ or more.

The state after the negative hydrogen ion is contained or introduced inthe treated material means that the negative hydrogen ion is confined inthe inner space of the cages of the C12A7 crystal. It is known that theunit lattice of the C12A7 crystal has a lattice constant of 1.119 nm,and a composition expressed by [Ca₂₄Al₂₈O₆₄]⁴⁺. Given that a positivecharge of +4 per unit lattice is entirely covered by the introduction ofthe negative hydrogen ion, it can be calculated that the number ofnegative hydrogen ions contained in the C12A7 crystal is a maximum of2.3×10²¹/cubic centimeter.

If the irradiated material in the electronically conductive state isheated to have a temperature of 200° C. or more, preferably 450° C., itwill be returned to a transparent/colorless insulative material, asshown in FIG. 3 (which shows the respective changes of absorbance andelectric conductivity relative to temperature in a single crystalobtained in Example 3). Further, if this insulative material isre-irradiated with ultraviolet ray or X-ray at a relatively lowtemperature of 200° C. or less, a colored conductive material can beobtained again. This conversion between the two state of the insulativematerial and the electronically conductive material can be repeatedlycarried out. The heating at a temperature of 550° C. or more causesdisappearance of the negative hydrogen ion from the crystal, resultingin neither generation of electronic conductance by means of irradiationwith ultraviolet light nor color development. In the colored state, boththe electronic conductance and color can also be erased by irradiatingthe material with high-intensity light having a wavelength correspondingto the color absorption band.

The above treated material exhibits no electronic conductance withoutirradiation with ultraviolet light. In this specification, this state isreferred to as “insulative state” or “insulative material”. As shown inFIG. 2, the material in the insulative state exhibits an ionicconductance derived from the negative hydrogen ion at a temperature ofgreater than the room temperature. While the insulative material has anionic conductivity of 10⁻¹⁰ Scm⁻¹ or less at the room temperature, itexhibits an ionic conductance equivalent to an ionic conductivity ofabout 10⁻⁴ Scm⁻¹. This ionic conductivity has a digit number greater byabout one than that of the ionic conductance exhibited by a conventionalC12A7 compound. If this conductive material is heated up to atemperature of 550° C. or more where the negative hydrogen ion is to belost, the ionic conductance derived from the negative hydrogen ion willbe lost, and any increase in electronic conductance by means ofirradiation with light will not be induced.

The material is formed with a pair of positive and negative electrodes,respectively, on the opposite surfaces thereof. Then, a given voltage isapplied between the electrodes to generate a negative hydrogen ion orhydrogen gas from the surface having the positive electrode.Alternatively, a first electrode is formed on one of the oppositesurface of the material. Then, in vacuum or arbitrary atmosphere, agiven voltage is applied between the first electrode and a secondelectrode disposed apart from the material by a given distance, in sucha manner that the first electrode on the side of the material serves asa negative electrode, so as to release a hydride ion from the materialas shown in FIG. 7.

EXAMPLE

The present invention will be described in more detail in connectionwith examples.

Example 1

A C12A7 single crystal prepared through a floating zone (FZ) process wasformed into a plate-shaped sample having a mirror finished surface and athickness of 300 μm. This sample was held in the flow of a mixed gasconsisting of 20 volume % of hydrogen and 80 volume % of nitrogen, at1300° C. for two hours, and then rapidly cooled in the same atmosphere.The heat-treated sample was irradiated with ultraviolet light of 254 nm(4.9 eV) at 1×10²⁰ photons/cm². FIG. 1 shows light absorption spectrumsbefore and after the ultraviolet irradiation. The white circular marksin FIG. 1 indicate evaluated values of light absorption speed, orphotosensitivity, obtained by changing the wavelength of ultravioletlight to be radiated.

Example 2

A C12A7 single crystal prepared through a floating zone (FZ) process wasformed into a plate-shaped sample having a mirror finished surface and athickness of 300 μm. This sample was held in the flow of a mixed gasconsisting of 20 volume % of hydrogen and 80 volume % of nitrogen, at1300° C. for two hours, and then rapidly cooled in the same atmosphere.The heat-treated sample was irradiated with light emitted from a Xe lampat a light intensity of 0.5 W/cm² and subjected to a processing foreliminating a wavelength of 340 nm or more, for 30 minutes or more untilthe change in light absorption was saturated. The irradiated sampleexhibited an enhanced electric conductivity having a digit numbergreater by about eight than that before the light irradiation. Thechange of electronic conductivity relative to temperature in the sampleafter the light irradiation is indicated by the block circular marks inFIG. 2. After completion of this measurement, the sample was heated upto 450° C., and returned to its original insulative state. At a roomtemperature, the sample exhibited an electric conductivity having adigit number reduced by about eight.

An ionic conductivity derived from a negative hydrogen ion in this stateis indicated by the white circular marks in FIG. 2. Then, thissingle-crystal sample was held in the air at 800° C. for 2 hours, andthen the ionic conductivity of the sample was measured. The measuredionic conductivity had a digit number reduced by about one. The changeof ionic conductivity relative to temperature in this measurement isindicated by the one-dot chain line in FIG. 2.

Example 3

A C12A7 single crystal prepared through a floating zone (FZ) process wasformed into a plate-shaped sample having a mirror finished surface and athickness of 300 μm. This sample was held in the flow of a mixed gasconsisting of 20 volume % of hydrogen and 80 volume % of nitrogen, at1300° C. for two hours, and then rapidly cooled in the same atmosphere.The heat-treated sample was irradiated with light emitted from a Xe lampat a light intensity of 0.5 W/cm² and subjected to a processing foreliminating a wavelength of 340 nm or more, for 4 minutes, and therebyconverted to an electrically conductive material having a color. Therespective changes of the absorbance and conductivity of this sample at440 nm and 850 nm were measured while heating the sample from a roomtemperature at a heating rate of 10° C./min. FIG. 3 shows themeasurement result. At about 400° C., the light absorption was lost, andthe electronic conductivity was reduced. That is, the sample lost thecolor based on photosensitivity, and returned to the insulative state.The increase of conductivity at 400° C. or more is based on thenegative-hydrogen-ionic conductance.

Example 4

A C12A7 polycrystal sample prepared through a solid-phase reactionprocess was held in the flow of a mixed gas consisting of 20 volume % ofhydrogen and 80 volume % of nitrogen, at 1300° C. for two hours, andthen rapidly cooled in the same atmosphere. The heat-treated sample waspounded to a slight degree in a mortar, and subjected to athermogravimetric and mass spectrographic (TG-MS) analysis testperformed at a heating rate of 110° C./m using He as a carrier gas. FIG.4 shows the change in the ionic current density of ions having the valuem/e=2 equivalent to a molecular hydrogen. At about 600° C., the releaseof molecular hydrogen in conjunction with the elimination of thenegative hydrogen ion from the C12A7 crystal was notably observed.

Example 5

A C12A7 single crystal prepared through a floating zone (FZ) process wasformed into a plate-shaped sample having a mirror finished surface and athickness of 300 μm. This sample was subjected to a heat treatment in anoxygen atmosphere at 1350° C. for 6 hours (sample A). Subsequently, thesample A was held in the flow of a mixed gas consisting of 20 volume %of hydrogen and 80 volume % of nitrogen, at 1300° C. for two hours, andthen rapidly cooled in the same atmosphere, so as to introduce anegative hydrogen ion into the C12A7 crystal (sample B). Subsequently,the sample B was heated in the air to have a temperature of 800° C. andthen cooled to eliminate the negative hydrogen ion or convert thenegative hydrogen ion to a hydroxyl group (sample C). The respectivehydroxyl group (OH⁻) concentrations of the samples A to C weredetermined from the infrared absorption intensity at 3560 cm⁻¹. Thiscalculation was performed using a molar absorbance coefficient of 90mol⁻¹ dm³ cm⁻¹. Further, the concentration of the total amount ofhydrogen contained in each of the samples A to C was quantitativelymeasured through secondary ion mass spectrometry (SIMS).

In the samples A and C, almost the entire hydrogen forms hydroxyl groupsas protons. In the sample B, the hydrogen exists in the form of not onlya proton but also a negative hydrogen ion. The concentration of thenegative hydrogen ion in the sample B can be estimated from ananalytical curve of proton concentration determined by the infraredabsorption intensities and the quantitative values obtained through theSIMS in the samples A and C. This calculation method is shown in FIG. 5.The concentration of hydrogen existing in the sample B in the form of anegative hydrogen ion was estimated to be 2×10²⁰ cm⁻³.

Example 6

A C12A7 polycrystal sample prepared through a solid-phase reactionprocess was held in the flow of a mixed gas consisting of 20 volume % ofhydrogen and 80 volume % of nitrogen, at 1300° C. for two hours, andthen rapidly cooled in the same atmosphere. The heat-treated sample waspounded to a slight degree in a mortar, and then irradiated withultraviolet light from a mercury lamp until the photosensitivity wassaturated. The respective states of the sample before and after theultraviolet irradiation were evaluated by electron spin resonance. Nosignal was observed before the ultraviolet irradiation. After theultraviolet irradiation, a signal of g=1.994 to 1.990 was observed. Itis believed that this signal is caused by F⁺ center. Considering incombination with the temperature dependence of electric conductanceobtained in Example 2, it is believed that the electric conductance inthis sample is caused by the variable-range hopping in an electron of F⁺center.

Example 7

A pellet-shaped C12A7 polycrystal sample prepared through a solid-phasereaction process was held in the flow of a mixed gas consisting of 20volume % of hydrogen and 80 volume % of nitrogen, at 1300° C. for twohours, and then rapidly cooled in the same atmosphere. The heat-treatedsample was held on a negative electrode placed on a vacuum tank, and apositive electrode was disposed at a position apart from the sample byabout 1 cm. Then, an electric field of 300 V·cm⁻¹ was applied betweenthe electrodes heating the sample at 710° C. A mass spectrum of ionsreleased from the sample during the application of the electric fieldwas measured using a time-of-flight mass spectrometer (TOF-MS). Themeasurement result is shown in FIG. 7.

Example 8

A plurality of pellet-shaped C12A7 polycrystal samples prepared througha solid-phase reaction process were subjected to a heat treatment indifferent hydrogen-containing atmospheres controlled at varioustemperatures as shown in Case Nos. 1 to 8 of Table 1, and cooled to aroom temperature at various cooling rates. Each of the heat-treatedsamples was irradiated with ultraviolet light from a Xe lamp for about30 seconds, and a resistance between two terminals spaced apart from oneanother by a distance of 2 mm was measured. Each of the resistancevalues in Table 1 is an electric resistance at a room temperature afterthe ultraviolet irradiation. Table 1 also shows the level of sensitivityto ultraviolet light (

: high, ∘: medium, x: none). As seen in Table 1, the polycrystal samplehas a higher conductance in response to the ultraviolet irradiation asthe sample is cooled at a higher cooling rate after subjected to a heattreatment in a hydrogen-containing atmosphere at a temperature of 800°C. or more.

TABLE 1 Sensitivity to Case Atmosphere Heat Treatment Cooling ResistanceUltraviolet 1 20% H₂—80% N₂ 1300° C. × 2 h slow cooling 10 kΩ

(200° C./h) 2 20% H₂—80% N₂ 1300° C. × 2 h furnace cooling 8 kΩ

(~600° C./h) 3 20% H₂—80% N₂ 1300° C. × 2 h rapid cooling 7 kΩ

(>50° C./h) 4 20% H₂—80% N₂ 1100° C. × 2 h furnace cooling 13 kΩ ∘(~600° C./h) 5 20% H₂—80% N₂  800° C. × 2 h furnace cooling 10¹⁰ Ω x(~600° C./h) 6 100% H₂ 1300° C. × 2 h rapid cooling 8 kΩ

(>50° C./h) 7 5% H₂—95% N₂ 1300° C. × 2 h rapid cooling 7 kΩ

(>50° C./h) 8 20% H₂—80% N₂  800° C. × 2 h rapid cooling 20 kΩ ∘ (>50°C./h)

Example 9

A pellet-shaped C12A7 polycrystal sample prepared through a solid-phasereaction process was held in the flow of a mixed gas consisting of 20volume % of hydrogen and 80 volume % of nitrogen, at 1300° C. for twohours, and then rapidly cooled in the same atmosphere. The heat-treatedsample was an insulative material having a resistance of 50 MΩ or morebetween 2 mm-spaced terminals at a room temperature. Then, the samplewas irradiated with X-ray having a photon energy of 1253.6 eV (target:Mg, filament current: 5A, acceleration voltage: 15 kV, cathode current:5 mA) for 1 hour. The irradiated sample was stained dark green, and theresistance between 2 mm-spaced terminals was reduced to 10 kΩ so as toexhibit an electronic conductance.

Example 10

An amorphous C12A7 film having a thickness of 200 nm was deposited on amagnesium oxide single crystal substrate through a pulsed-laserdeposition process using a C12A7 sintered body as a target and an ArFexcimer laser as a light source. This film was subjected to a heattreatment in the normal atmosphere at 1000° C., and thereby converted toa crystalline C12A7 thin film. Further, the crystalline thin film washeld in an atmosphere consisting of 20 volume % of hydrogen and 80volume % of nitrogen, at 1200° C. for 1 hour, and then rapidly cooled.Then, the one-half region of the obtained thin film was irradiated withultraviolet light from a Xe lamp at a room temperature. As a result, theregion irradiated with the ultraviolet light was a semiconductormaterial having a conductivity of 0.1 Scm⁻¹, and the remaining regionwithout the irradiation was an insulative material having a conductivityof 10⁻⁸ Scm⁻¹ or less. The thin film was transparent and colorless inappearance even after the ultraviolet irradiation. This proved that atransparent electronically conductive region can be formed on atransparent insulative thin film by means of irradiation withultraviolet light.

INDUSTRIAL APPLICABILITY

While the material of the present invention in the form of a bulkcrystal or polycrystal having a conductivity of about 1 Scm⁻¹ is stainedgreen by irradiation with ultraviolet light, the material in the form ofa thin film having a thickness of about 200 nm can be used as acolorless transparent electrode or transparent wiring because it has amaximum absorption rate of about 1% in the visible region. Indium inindium oxides most frequently used as the material of transparentelectrodes is a sparse resource. In contrast, calcium and aluminum areextremely easily obtainable materials, and significantly low inenvironmental load.

In the material of the present invention, a specific region in itsinsulative state can be selectively formed as an electrically conductiveregion by means of irradiation with ultraviolet light. Thus, thematerial can be exposed to light of a circuit pattern to form a2-dimensional electronic circuit on the surface thereof. In addition,X-rays having a shorter wavelength can be used as a light source to forma further microscopic circuit pattern.

A laser beam can be focused on the inside of the material of the presentinvention by utilizing two-photon absorption according to avisible-light laser to freely form an optically writable 3-dimensionalelectronic circuit not only on the surface of the material but also inthe inside of the material. The formed circuit pattern can be erasedentirely or partly by means of irradiation with high-intensity lighthaving a wavelength equivalent to a color absorption band, heating ofthe entire material, or Joule's heat arising from a large currentapplied to the circuit. That is, an optically writable and erasable3-dimesional electronic circuit can be formed.

Based on the above writing and erasing means, the material of thepresent invention can be applied to a 3-dimensional storage elementserving as a main component for a storage device, which has a pluralityof access means, such as a writing means using ultraviolet light, areading means using visible/infrared light or electric resistance, andan erasing means using current application, visible/infrared lightradiation or heating.

In the material of the present invention, the characteristic as aion-conductive material capable of conducting a negative hydrogen ioncomprising a primary component of a hydride ion, and the characteristiccapable of releasing the negative hydrogen ion to a vacuum space or anarbitrary atmosphere by means of an electric field can be utilized toperform a selective reduction reaction or hydrogenation reaction. Thatis, the material of the present invention can act as a negative hydrogenion-conducting solid-electrolyte.

1. A 12CaO.7Al₂O₃ compound, which incorporates a negative hydrogen ion(H⁻, H²⁻, H₂ ⁻) at a concentration of 1×10¹⁸ cm⁻³ or more, which has anelectronic conductance equivalent to an electric conductivity of 10⁻⁵Scm⁻¹ or more at a room temperature.
 2. A 12SrO.7Al₂O₃ compound, whichincorporates a negative hydrogen ion (H⁻, H²⁻, H₂ ⁻) at a concentrationof 1×10¹⁸ cm⁻³ or more, which has an electronic conductance equivalentto an electric conductivity of 10⁻⁵ Scm⁻¹ or more at a room temperature.3. A mixed crystal compound of 12CaO.7Al₂O₃ and 12SrO.7Al₂O₃, whichincorporates a negative hydrogen ion (H⁻, H²⁻, H₂ ⁻) at a concentrationof 1×10¹⁸ cm⁻³ or more, which has an electronic conductance equivalentto an electric conductivity of 10⁻⁵ Scm⁻¹ or more at a room temperature.4. A method of producing the compound as defined in claim 1, comprisingsubjecting a 12CaO.7Al₂O₃ compound, to a heat treatment at a temperatureof 800° C. or more in an atmosphere containing 1000 ppm or more ofhydrogen, to thereby clathrate a negative hydrogen ion (H⁻, H²⁻, H₂ ⁻)into said selected compound at a concentration of 1×10¹⁸ cm⁻³ or more,and further irradiate said selected compound with ultraviolet ray orX-ray.
 5. A method of producing the compound as defined in claim 2,comprising subjecting a 12SrO.7Al₂O₃ compound to a heat treatment at atemperature of 800° C. or more in an atmosphere containing 1000 ppm ormore of hydrogen, to thereby clathrate a negative hydrogen ion (H⁻, H²⁻,H₂ ⁻) into said selected compound at a concentration of 1×10¹⁸ cm⁻³ ormore, and further irradiate said selected compound with ultraviolet rayor X-ray.
 6. A method of producing the compound as defined in claim 3,comprising subjecting a mixed crystal compound of 12CaO.7Al₂O₃ and12SrO.7Al₂O₃ to a heat treatment at a temperature of 800° C. or more inan atmosphere containing 1000 ppm or more of hydrogen, to therebyclathrate a negative hydrogen ion (H⁻, H²⁻, H₂ ⁻) into said selectedcompound at a concentration of 1×10¹⁸ cm⁻³ or more, and furtherirradiate said selected compound with ultraviolet ray or X-ray.
 7. Thecompound as defined in any one of claims 1 to 3, wherein the compound isincluded in a transparent electrode or wiring.
 8. The compound asdefined in any one of claims 1 to 3, wherein the compound is included inan optically writable and erasable 3-dimensional electronic circuit and3-dimensional storage element.
 9. The compound as defined in any one ofclaims 1 to 3, wherein the compound is included in anegative-hydrogen-ion-conducting solid-electrolyte.